U.S. patent number 4,192,935 [Application Number 06/000,170] was granted by the patent office on 1980-03-11 for ethylene polymers of high melt index.
This patent grant is currently assigned to DuPont of Canada Limited. Invention is credited to Peter J. Lovell, Ian C. B. Saunders.
United States Patent |
4,192,935 |
Lovell , et al. |
March 11, 1980 |
**Please see images for:
( Certificate of Correction ) ** |
Ethylene polymers of high melt index
Abstract
An ethylene polymer having a density in the range of about
0.940-0.960, a melt index in the range 100-200 and a ratio of
weight-average molecular weight to number-average molecular weight
of less than 5 is disclosed. The polymer is a copolymer of ethylene
and at least one .alpha.-olefin having 4-10 carbon atoms e.g.
butene-1, hexene-1 or octene-1. The preferred polymer is a
copolymer of ethylene and butene-1. The polymers may be used in the
injection molding of thin-wall containers e.g. containers having a
wall thickness of less than 0.7 mm, especially a thickness of less
than 0.5 mm and in particular a thickness of less than 0.4 mm.
Inventors: |
Lovell; Peter J. (Kingston,
CA), Saunders; Ian C. B. (Sarnia, CA) |
Assignee: |
DuPont of Canada Limited
(Montreal, CA)
|
Family
ID: |
9705764 |
Appl.
No.: |
06/000,170 |
Filed: |
January 2, 1979 |
Foreign Application Priority Data
|
|
|
|
|
Jan 6, 1978 [GB] |
|
|
00517/78 |
|
Current U.S.
Class: |
526/348.6;
264/325; 526/348.2; 526/348.3; 526/348.7 |
Current CPC
Class: |
B29C
45/0001 (20130101); C08F 210/16 (20130101); C08L
23/0815 (20130101); C08F 210/16 (20130101); C08F
210/08 (20130101); C08F 2500/12 (20130101); C08F
2500/03 (20130101) |
Current International
Class: |
B29C
45/00 (20060101); C08L 23/00 (20060101); C08F
210/00 (20060101); C08L 23/08 (20060101); C08F
210/16 (20060101); C08F 210/02 (); C08F
210/16 () |
Field of
Search: |
;526/348.6,348.2,348.3,348.7 |
Foreign Patent Documents
Primary Examiner: Levin; Stanford M.
Claims
We claim:
1. An ethylene polymer having a density in the range of about
0.940-0.960, a melt index in the range 100-200 and a ratio of
weight-average molecular weight to number-average molecular weight
of less than 5, said polymer being a copolymer of ethylene and at
least one .alpha.-olefin having 4-10 carbon atoms, the
.alpha.-olefin being an aliphatic hydrocarbon.
2. The polymer of claim 1 in which the melt index is in the range
100-150.
3. The polymer of claim 2 in which the ratio of weight-average
molecular weight to number-average molecular weight is less than
3.5.
4. The polymer of claim 3 in which the polymer is a copolymer of
ethylene and an .alpha.-olefin having 4-8 carbon atoms.
5. The polymer of claim 3 in which the polymer is a copolymer of
ethylene and butene-1.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ethylene polymers of high melt
index and in particular to ethylene/.alpha.-olefin copolymers
having a melt index of at least 100 and especially in the range
100-200.
2. Description of the Prior Art
Melt index is a measure of melt viscosity which is related to the
molecular weight of the polymer. As referred to herein the melt
index of a polymer is that measured by the method of ASTM D-1238
(condition E).
Ethylene homopolymers and ethylene/.alpha.-olefin copolymers, in
which the .alpha.-olefin is an aliphatic hydrocarbon, are sometimes
referred to as polyethylenes. Such polyethylenes are capable of
being used in a wide variety of end uses, the end use depending in
particular on the physical properties of the polymer. One such
physical property is the melt index of the polymer. Polymers of
relatively low melt index, for example, less than about 10 and
especially less than about 1 and having a density of about
0.915-0.960 may be extruded in the form of film. Such film may be
used as a packaging material.
Polyethylene is also capable of being fabricated into articles by
moulding techniques especially injection moulding techniques.
Moulding grade polyethylene is usually of higher melt index than
that used in the manufacture of film. Typically, the melt index of
polyethylene used in injection moulding processes is in the range
of about 0.3 to 45 while the density is usually in the range of
about 0.915 to 0.965. However an ethylene/.alpha.-olefin polymer
containing less than 0.1% of butene-1 as the .alpha.-olefin and
having a melt index of 85 and a density of 0.959 is commercially
available as an injection moulding resin.
Examples of articles that may be manufactured by injection moulding
processes are containers especially containers that are used for
the packaging of ice cream, yogurt, margarine and the like. Such
containers should be of relatively uniform thickness and should
have a surface that is acceptable to the consumer. The economics of
the manufacture of containers by injection moulding processes
depend at least in part of the thickness of the walls of the
container, especially the minimum thickness consistent with the
manufacture of containers of acceptable appearance and physical
properties, and the rate, e.g., cycle time, at which such
containers may be manufactured. Small containers tend to be of
lower wall thickness than larger containers as less flow of polymer
is required during the injection moulding process in order to fill
the mould. Typical wall thicknesses of containers manufactured in
injection moulding processes are at least 0.7 mm. Attempts to
manufacture containers of lower wall thickness e.g., less than 0.5
mm, have generally been unsuccessful especially because of process
problems that result in incompletely fabricated containers,
containers having non-uniform wall thickness as a result of process
problems and/or containers of poor surface appearance. It is an
object of the present invention to provide polyethylenes of
improved processability, especially in injection moulding
processes, and in particular for the manufacture of containers
having a wall thickness of less than about 0.7 mm.
SUMMARY OF THE PRESENT INVENTION
Accordingly, the present invention provides an ethylene polymer
having a density in the range of about 0.940-0.960, a melt index in
the range 100-200 and a ratio of weight-average molecular weight to
number-average molecular weight of less than 5, said polymer being
a copolymer of ethylene and at least one .alpha.-olefin having 4-10
carbon atoms, the .alpha.-olefin being an aliphatic
hydrocarbon.
In an embodiment of the polymer of the present invention, the ratio
of weight-average molecular weight to number-average molecular
weight is less than 3.5.
In a further embodiment the polymer is an ethylene/butene-1
copolymer.
The present invention also provides in a process for the
manufacture of containers having a wall thickness of less than 0.7
mm, said containers being manufactured from thermoplastic polymer
by injection moulding said polymer, the improvement comprising
using as the thermoplastic polymer an ethylene polymer having a
density in the range of about 0.940-0.960, a melt index in the
range 100-200 and a ratio of weight-average molecular weight to
number-average molecular weight of less than 5, said polymer being
a copolymer of ethylene and at least one .alpha.-olefin having 4-10
carbon atoms, the .alpha.-olefin being an aliphatic
hydrocarbon.
DETAILED DESCRIPTION OF THE INVENTION
Polyethylenes capable, in particular, of being fabricated by
injection moulding processes into containers having a reduced wall
thickness and/or having improved flow properties in moulding
processes have now been found.
The ethylene polymer of the present invention is a copolymer of
ethylene and at least one .alpha.-olefin of 4-10 carbon atoms, such
.alpha.-olefins being aliphatic hydrocarbons. The preferred
.alpha.-olefins having 4-8 carbon atoms, for example, butene-1,
hexene-1 and octene-1. In a preferred embodiment the copolymer is a
copolymer of ethylene and only one .alpha.-olefin, especially where
the .alpha.-olefin is butene-1.
The polymers of the present invention have melt indices in the
range of about 100-200. In a preferred embodiment the polymers have
melt indices in the range 100-150.
The density of the polymers of the present invention may be in the
range of about 0.940-0.960, the density being determined primarily
by the amount of .alpha.-olefin in the polymer. When the
.alpha.-olefin is butene-1 the above range of density corresponds
to a range of about 0.2-2.0% by weight of butene-1 in the
copolymer. The density of the polymer is that measured by the
method of ASTM D-1505.
The polymers of the present invention are also characterized by a
ratio of weight average molecular weight (M.sub.w) to number
average molecular weight (M.sub.n) of less than about 5. Preferably
the ratio of M.sub.w :M.sub.n is less than about 3.5. The ratio of
M.sub.w :M.sub.n may be determined by gel permeation
chromatography.
The polymers of the present invention are capable of being used in
a variety of uses. In particular the polymers are capable of being
used in the manufacture of containers especially in the manufacture
of containers by injection moulding techniques. The polymers may be
used in the manufacture of containers having a wall thickness of
less than 0.7 mm, especially less than 0.5 mm, and in particular
less than 0.4 mm. The design of the containers manufactured from
the polymers of the present invention is more critical than the
design of containers manufactured from polymers of lower melt
index. For example, the containers should be designed so as to
eliminate or reduce "stress-points" e.g., the junction of the
bottom of the container and the walls of the container should be
smoothly rounded and not angular. Such design will be understood in
the art. Containers manufactured with high melt index polymers tend
to have a uniform polymer density and to be substantially free of
stresses in comparison to containers of conventional polymers.
The polymers of the present invention are copolymers and not
homopolymers. Containers injection moulded from ethylene
homopolymers having a density of greater than 0.960 and a high melt
index tend to be more susceptible to brittleness and to cracking
when flexed. Containers injection moulded from the copolymers of
the present invention are substantially more resistant to cracking
when flexed.
The polymers of high melt index preferably contain antioxidants
known for polymers of ethylene. The polymers of the present
invention may also contain pigments of the kind used for
conventional polyethylenes.
The polymers of the invention may be polymerized from the monomers
using a process of the type disclosed in Canadian Pat. No. 856,137
which issued on Nov. 17, 1970 to W. E. Baker, I. C. B. Saunders and
J. M. Stewart. In such a process ethylene monomer admixed with
.alpha.-olefin is dissolved in an inert solvent, for example,
cyclohexane, and introduced into a reaction zone. The monomers are
copolymerized in the reaction zone in the presence of a
co-ordination catalyst which is separately injected in solvent into
the reaction zone. Pressure and temperature are controlled so that
the polymer formed remains in solution. Hydrogen may be added to
the feed at a rate of, for example, 40-120 parts per million by
weight based on the reactor feed, in order to obtain and control
the melt index and/or molecular weight distribution. The
polymerization catalyst is usually deactivated immediately after
the ethylene copolymer leaves the reaction zone.
Catalysts useful for the preparation of the polymers are the
so-called co-ordination catalysts. These catalysts may, for
example, be obtained by mixing a compound of titanium or zirconium
preferably one in which the said metals are attached to groups such
as -oxyhydrocarbon, -halide or any combination thereof, with an
organometallic reducing agent as the second component. The catalyst
used may, for example, be composed of a titanium halide and a
reducing component such as an aluminum alkyl. Preferred catalyst
combinations are titanium tetrachloride and aluminum triethyl, or a
mixture of vanadium oxychloride, titanium tetrachloride and
aluminum triisoprenyl.
After deactivation of the catalyst the polymer may be passed
through a bed of activated alumina or bauxite which removes
substantially all of the deactivated catalyst residues. The solvent
may then be flashed off from the polymer and the polymer extruded
into water and cut into pellets or other suitable comminuted
shapes.
The present invention is illustrated by the following examples. In
the examples melt index was measured according to the
aforementioned ASTM procedure except that, because of the high flow
rates of the polymers, a weight of 1060 g was used. Melt index was
then determined from an extrapolated calibration curve obtained
using polymers having a melt index of less than 100.
All parts and percentages are by weight, unless otherwise
specified.
EXAMPLE I
A mixture of ethylene and butene-1 in cyclohexane solution were
copolymerized in a commercial-scale stirred autoclave reactor in
the presence of a catalyst comprising vanadium oxytrichloride,
titanium tetrachloride and aluminum isoprenyl. Hydrogen was fed to
the reactor. The reaction was terminated using an organic acid
deactivator and the polymer was subsequently separated from the
cyclohexane.
Further experimental details and the results obtained are given in
Table I.
TABLE I ______________________________________ Run No. 1 2 3 4 5
______________________________________ Feed Ethylene (%) 17.8 17.7
17.8 18.0 18.0 Butene (%) 4.4 4.4 4.4 17 17 Hydrogen (ppm) 87 96
112 82 61 Temperature (.degree.C.) Inlet 58 58 80 56 56 Outlet 278
279 288 279 279 Ethylene Conversion (%) 96.4 96.1 97.1 94.4 94.4
Polymer Density (g/cm.sup.3) 0.957 0.958 0.960 0.947 0.947 Melt
Index 100 117 190 126 104 M.sub.w /M.sub.n * NA NA NA 3.1 NA
______________________________________ NA = not available, values
believed to be about 3.0 *obtained by gel permeation
chromatography, calibrated with university contact resins obtained
from E.I. du Pont de Nemours and Company, Wilmington, Delaware,
U.S.A. A sample of polymer having a density of 0.94 and a melt
index of 166 had a M.sub.w /M.sub.n of 3.0.
EXAMPLE II
Using an ethylene/butene-1 polymer of the invention, having a
density 0.958 and melt index of 138, containers having a wall
thickness of 0.58 mm were moulded in a commercial-scale high speed
injection moulding process. Melt temperatures were not measured.
However all zone and nozzle temperatures were about 55.degree. C.
lower than those necessary to process a commercial polyethylene of
melt index of 60 using the same mould. Cycle times were reduced
from about 5.2 seconds per container, using the commerical
polyethylene resin, to about 4.1 seconds per container when the
polyethylene of melt index of 138 was used. The containers were of
500 ml capacity, of a type used for packaging food, and had a shape
which was recognized as imparting poor impact strength to the
container e.g. had a lip, stacking shoulder and base cross-sections
which were angular.
Samples of the containers were filled with water and a lid was
placed on the containers. The filled containers were dropped, bases
down, onto a concrete floor from various heights. No containers
broke when dropped from a height of 1.5 m.
Further samples of the containers were placed on a concrete floor
and crushed underfoot. Only one or two splits in each container
were observed.
EXAMPLE III
Using an ethylene/butene-1 polymer of the invention, having a
density 0.949 and melt index of 105, containers having a wall
thickness of 0.58 mm were moulded in a commercial-scale high speed
injection moulding process. Melt temperatures were not measured.
However all zone and nozzle temperatures were about 55.degree. C.
lower than those necessary to process a commercial polyethylene of
melt index of 60 using the same mould. Cycle times were reduced
from about 5.2 seconds per container, using the commercial
polyethylene resin, to about 4.1 seconds per container when the
polyethylene of melt index of 105 was used. The containers were of
500 ml capacity used for packaging food, and had a shape which was
recognized as imparting poor impact strength to the container e.g.
had a lip, stacking shoulder and base cross-sections which were
angular.
Samples of the containers were filled with water and a lid was
placed on the containers. The filled containers were dropped, bases
down, onto a concrete floor from various heights. No containers
broke when dropped from a height of 1.5 m.
Further samples of the containers were placed on a concrete floor
and crushed underfoot. No cracks were observed in any of the
containers.
EXAMPLE IV
Using the procedure described in Example I ethylene and butene-1
were copolymerized to yield a polymer having a density of 0.959, a
melt index of 138 and a ratio of M.sub.w /M.sub.n of less than 5.0.
Details of the copolymerization process were as follows:
Feed: Ethylene 17.8%, Butene-1 4.4%, Hydrogen 95 ppm.
Temperature: Inlet 58.degree. C., Outlet 278.degree. C.
Ethylene Conversion 96.4%.
The polymer obtained was ground to a fine powder, dry blended with
1000 ppm of talc and re-extruded into pellets. Containers having a
wall thickness of 0.36 mm were moulded from the pellets in a
commercial-scale high speed injection moulding process using an
experimental four cavity mould. The containers were of 500 ml
capacity and of a shape which was recognized as imparting poor top
loading strength but reasonable impact strength e.g. rounded base
cross-sections and a filleted stacking shoulder. Acceptable
containers were moulded at a cycle time of 4.0 seconds.
Samples of the containers were filled with water, lidded and
dropped, base down, onto a concrete floor. An F.sub.50 i.e the
height were 50% of the containers failed, of one meter was
obtained.
Further samples of the container were top loaded with a 30 lb.
weight. After 2 hours buckling was observed and after 24 hours all
containers were completely crushed.
In the light of the above the containers are capable of being used
in a wide variety of packaging end-uses, e.g. for the packaging of
food and small articles.
* * * * *